1. Field of the Invention
The present invention relates to an apparatus and a method for pressing and combining two substrates of an LCD (liquid crystal display) panel. In particular, the present invention relates to an apparatus and a method for improving the uniformity of gap width between the two substrates.
2. Description of the Related Art
In general, an LCD panel has two substrates, one front and one rear, having electrodes and a liquid crystal layer between the two substrates combined by a sealant.
After processing the front substrate and the rear substrate and forming electrodes on the inner surfaces of the two substrates, spacers (not shown) are dispersed on the inner surfaces of one of the substrates. A sealant (not shown) having an injection hole is printed on the inner surface of one of the substrates near the edge of the substrates. Next, the two substrates are combined with each other through hot press process, and the spacers give a cell gap between the two substrates. A liquid crystal material is injected into the cell gap to form a liquid crystal layer. Finally, the cell is completed by filling up the injection hole with a sealant.
The gap widths at different locations of the cell gap influence the intensity of the electric fields between electrodes when the liquid crystal cell is supplied with electric power, and will, subsequently, affect the performance of the liquid crystal cell. The electric fields must be both uniform and within an acceptable range. Therefore, manufacturers must generate not only a cell gap with an acceptable range, but also well-controlled uniformity.
A conventional method for hot press provides a uniform pressure distribution to press the two substrates and uniform heating power distribution to harden the sealant combining the two substrates. The simple hypothesis of this method is that a uniform control parameter distribution introduces a uniform cell gap. FIG. 1 illustrates the operation of a conventional hot press process. The front substrate 10 and the rear substrate 12 are going to be combined. A pressure plate 16 and a platform 14 uniformly press and heat the two substrates until the sealant between is hardened, thereby obtaining a cell gap with an excellent uniformity.
In fact, however, the hypothesis of the convention method rarely holds in practice. The sealant, for example, may have tiny quality or quantity variations in different places, as may the spacers. Even the substrates may have uneven surfaces. Therefore, though pressure and heating distribution on the substrates may be uniform, the cell gap may not be uniform enough, producing a faulty LCD panel.
Therefore, an object of the present invention is to optimize the uniformity of a cell gap by, during pressing, monitoring the gap width distribution and modifying process parameters to fine-tune the cell gap.
An aspect of the present invention provides a method for controlling gap widths. This method is applied during the combining of the first and second substrates. The first substrate has a plurality of measured points. The gap widths lie between the first and second substrates at the measured points. The first step of the method is to provide a control parameter distribution for pressing and combining the first and second substrates. The second step of the method is to measure, during pressing and combining of the first and second substrates, the gap widths. The final step of the method is to modify, when the gap widths don""t meet a predetermined requirement, the control parameter distribution to adjust the gap widths.
Another aspect of the present invention provides an apparatus for pressing and combining first and second substrates. The apparatus comprises a controller, a pressing means and a monitoring means. The controller controls parameter distribution. The pressing means, according to the parameter distribution, presses and combines the first substrate and the second substrate. The monitoring means measures gap widths between the first substrate and the second substrate, each gap width corresponding to one of measured points on the first substrate. When the gap widths don""t meet a predetermined requirement, the controller changes the parameter distribution and, subsequently, modifies the gap widths.
The parameter distribution can be any parameter distribution that controls the hot press process, such as temperature distribution, pressure distribution, heating power distribution, or others.
The predetermined requirement can be any product requirement that the gap widths must meet. The requirement of uniformity of the cell gap is selected as an example.
The benefits of the present invention include the improvement of uniformity of the cell gap. During pressing of the two substrates, gap widths at measured points are monitored and fed back to modify parameter distribution, thereby turning out a cell gap with excellent uniformity. By such a feedback algorithm, the stability and the uniformity of the cell gap can be optimized.